HAMBURG, Germany — Hangar doors slid open to reveal a fleet of white Mercedes-Benz vehicles arrayed on a rain-slicked runway.

As fireworks shot skyward, an imposing gray sedan zoomed forward onto a temporary stage, delivering Alicia Keys, in a dark floor-length evening gown, to the piano where she performed with a local backup band, the Hamburg Symphony.

Befitting the flagship of the Mercedes line, the premiere of the new S-Class at a vast Airbus jetliner factory here on Wednesday night was a grandiose event. Always a showcase for luxury appointments, this latest incarnation of the S-Class is notable for much more than features like the so-called hot-stone massages offered by its reclining rear seats. Or the Wi-Fi. Or the cup holders that keep drinks warm or cold.

The 2014 S-Class, which goes on sale in September at an estimated starting price of $100,000, is a significant advance in the development of autonomous autos. That is, while it still requires a human behind the steering wheel, in the right conditions the car can steer itself through city traffic or drive on the highway at speeds upward of 120 miles an hour using an array of radar, infrared and optical sensors to track lane markings or the car ahead — even around curves.

“It marks the beginning of autonomous driving,” said Dieter Zetsche, chief executive of Daimler, the parent company of Mercedes-Benz.

There might be an element of hyperbole in that statement. But certainly the S-Class, which can also park itself, brake automatically to avoid hitting humans or other cars and sense when a driver is becoming fatigued, is a further evolution of systems intended to relieve some of the tedium of driving.

The optional system is analogous to the autopilots that enable airliners to carry out many of the routine tasks of flight and cruising but still require a human pilot to keep an eye on things. Future upgrades of the Mercedes S-Class will enable the car to automatically change lanes at autobahn speeds.

Along with BMW and Audi, its German luxury rivals, Mercedes is pushing technology ever closer toward a virtual chauffeur. BMW later this year plans to roll out a similar system in its i3 electric city car, and soon after in the 7 Series luxury sedan.

Most major carmakers are working on some form of self-driving capability. The 2013 Lincoln MKZ has a system that keeps the car in lane and maintains a set distance from the vehicle ahead. But unlike the Lincoln, the Mercedes is programmed to hold the car in the middle of the lane, rather than just correcting if the driver drifts out of line.

Still, German engineers are skeptical of predictions by Google engineers and others that within five years vehicles will be driving themselves from the garage to the grocery store without human intervention. It will take a decade, maybe more, to solve all the technological and legal problems, they say.

“We think we still have quite a bit of work ahead of us,” said Werner Huber, director of driver assistance technology at BMW.

It is logical that German carmakers would be leading the way toward vehicles that can drive themselves. Their well-heeled customers are willing and able to pay for a feature that would, for instance, let them check a stock portfolio online while stuck in traffic, rather than staring at the taillights ahead.

Even BMW executives are willing to admit that there are times when the company’s longtime German marketing slogan of “Freude am Fahren,” which translates to the joy of driving, doesn’t apply.

“In a lot of situations you don’t have any joy in driving,” Mr. Huber said during a recent interview in the plain brick building in Munich that houses his research team. His group includes engineers, software specialists, sensor experts and psychologists. “The joy is in being driven,” he said.

Self-driving cars might one day also offer mobility to people who are unable to drive because of age or handicaps. Google, applying its expertise in artificial intelligence, created a stir last year with a video that showed a blind man at the wheel of one of the company’s self-driving vehicles. The implication is that self-driving cars are close to reality.

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SELF-DIRECTED The 2014 Mercedes-Benz S-Class will offer a system that gives drivers a break by steering the car.CreditMercedes-Benz USA

David L. Strickland, administrator of the National Highway Traffic Safety Administration, referred to the timeline suggested by Google on Wednesday in his testimony before the Senate Committee on Commerce, Science and Transportation.

“What was once previously thought of as science fiction and decades away from reality may now appear to be just around the corner,” Mr. Strickland said, according to a text of his remarks.

The more cautious assessment of self-driving technology by Mr. Huber and others partly reflects the classic Spock-vs.-Kirk difference in mentality between Germany’s rational, data-driven engineers and the visionaries of Silicon Valley.

Who proves to be right could have major implications for society. At least in theory, self-driving cars would be safer, able to react more quickly than humans to avoid danger and use less fuel.

But German engineers point out they are a long way from having software that can do things that come natural to humans — for instance, judging whether a person standing at a street corner is about to cross the road or is just waiting for a bus.

There are also myriad legal issues which must be resolved by governments and insurance companies. If a car gets in an accident while on autopilot, who pays the damage, the car’s owner or the automaker? The questions about liability are one reason that the Mercedes system requires the driver to keep at least one hand on the steering wheel.

Mr. Zetsche, the Daimler chief executive, said that experimental Mercedes technology already enables a car to drive itself from one place to another without human intervention, though more work remains to ensure the system is totally reliable.

It might take longer to perfect the legal framework than the software, he said.

“Certainly in a decade I would sit in a car — a Mercedes car — and let the car go from A to B,” Mr. Zetsche said in a brief interview at the S-Class introduction. “We might still struggle with the legal challenges.”

A recent ride in a self-driving BMW research car illustrated some of the hurdles. The test vehicle, a 5 Series sedan loaded with a dozen unobtrusive sensors, handled heavy autobahn traffic outside Munich with aplomb. It slowed down to let a Ford Fiesta merge into traffic from an onramp, for example. It read traffic signs and adjusted the car’s speed automatically.

But the logic-driven BMW had trouble gauging the intentions of erratic humans. When a vehicle in the lane to the left slowed down for no apparent reason, the BMW slowed down too in order to avoid passing on the right. A human being might not have interpreted the rules of the road so literally.

Mr. Huber said that more sophisticated sensors were needed to make it possible for cars to analyze everything that is happening on the road and react more like a human driver would.

As part of its autonomous driving program, Audi, a unit of the Volkswagen Group, is working on a system that would enable cars to drive themselves into a parking garage and find an empty space without a human aboard — a threat to valet parking attendants everywhere. But the system requires specially equipped garages.

Autonomous driving will be easier to manage when car companies work out standards that would let cars share information like location and speed among themselves.

Cost is another obstacle. Self-driving technology will not be feasible until the equipment itself is affordable. The expense of research and development is one reason BMW formed a partnership with a German components supplier, Continental, to develop what it calls the Connected Drive systems.

Alejandro Vukotich, head of development for driver assistance systems at Audi, pointed out that predictions of utopian technological progress are notoriously unreliable. He recalled reading an article in National Geographic as a boy that predicted cars would be driving themselves by the year 2000.

“We have passed the year 2000,” Mr. Vukotich noted.

He and others see the path to fully automated driving as gradual. “It’s difficult to make a prognosis,” he said. “We will get closer step by step.”

The S-Class sedans is expected to expand into a full range of models, including hybrids and diesels, with United States dealers offering first the S550 sedan, followed by an all-wheel drive version and an AMG performance model in November.

Correction:

An article in some editions last Sunday about the gala introduction of the 2014 Mercedes-Benz S-Class misidentified the orchestra that accompanied the singer Alicia Keys. It is the Hamburg Symphony, not the Hamburg Philharmonic.